1. Field of the Invention
The present invention relates to a method for manufacturing trench MOSFET device and the structure thereof, in particular, to a method for manufacturing trench MOSFET device with low gate charge.
2. Description of Related Art
Trench metal-oxide-semiconductor (MOS) device includes a gate electrode inside a trench which extends downward from a surface of the semiconductor substrate. The current flow by the gate electrode of the trench MOS device is substantially along a vertical direction. Therefore, cell pitch of the MOS devices can be reduced. In present, there are various MOS devices available in the market, such as metal-oxide-semiconductor field-effect transistor (MOSFET), insulated-gate bipolar transistor (IGBT), thryistor, and so on.
As the operating frequency of the power switching devices such as MOSFET increased, improvement of switching efficiency becomes more and more important. How to design a switching device with improved switching rate and reduced switching loss has become an object in the industry. In view of the characteristics of semiconductors, switching rate and switching loss can be improved by lowering the capacitance between gate and drain (Cgd).
In a conventional MOSEFT device, the trenches are filled with ploy-silicon material which acts as the gate, and the ploy-silicon material is disposed on the bottom and the side-wall of the trenches. The capacitance between gate and drain of the MOSFET device depends on the bottom area of the trenches. The size of the bottom area can be decreased by using a narrower gate to improve switching loss for high frequency applications. However, the narrower gate may result in a greater gate resistance to cause energy loss.